scholarly journals Fracture Propagation Characteristic and Micromechanism of Rock-Like Specimens under Uniaxial and Biaxial Compression

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Xue-wei Liu ◽  
Quan-sheng Liu ◽  
Shi-bing Huang ◽  
Lai Wei ◽  
Guang-feng Lei
Keyword(s):  
Fractured Rock ◽  
Fracture Propagation ◽  
Propagation Characteristic ◽  
Propagation Path ◽  
Biaxial Compression ◽  
Compression Tests ◽  
Microdamage Accumulation ◽  
Macroscopic Fracture ◽  
Crack Tips ◽  
Ae Location

This paper presents a set of uniaxial and biaxial compression tests on the rock-like material specimens with different fracture geometries through a rock mechanics servo-controlled testing system (RMT-150C). On the basis of experimental results, the characteristics of fracture propagation under different fracture geometries and loading conditions are firstly obtained. The newly formed fractures are observed propagating from or near the preexisting crack tips for different specimens, while the propagation paths are affected by the loading condition obviously. Then, by adopting acoustic emission (AE) location technique, AE event localization characteristics in the process of loading are investigated. The locations of AE events are in good agreement with the macroscopic fracture propagation path. Finally, the micromechanism of macroscopic fracture propagation under uniaxial and biaxial compression conditions is analyzed, and the fracture propagation can be concluded as a result of microdamage accumulation inside the material. The results of this paper are helpful for theory and engineering design of the fractured rock mass.

Influence of Joint Set with Different Angles on Rock Behaviour and Cavern Stability

2011 ◽  
Vol 90-93 ◽  
pp. 662-665
Author(s):  
Hai Ping Ma ◽  
Jing Wang ◽  
Wei Shen Zhu ◽  
Min Yong
Keyword(s):  
Fracture Process ◽  
Fractured Rock ◽  
Biaxial Compression ◽  
Compression Tests ◽  
Rock Samples ◽  
Rock Stability ◽  
Confining Pressures ◽  
Initiation Stress ◽  
Cavern Stability

Using DDARF method, the uniaxial and biaxial compression experiments of double-fractured rock samples are numerically investigated. Influences of different fracture angles and confining pressures on behaviour of rock samples are studied. Moreover, the fracture process, the crack initiation stress, and the peak strength of the fractured rock under both uniaxial and biaxial compression tests are obtained. The results are used to obtain the strength envelope and to analyze the rock stability of an underground project as a case study.

scholarly journals A Constitutive Model for Locally Drained Shear Bands in Globally Undrained Dense Sand

2019 ◽  
Vol 92 ◽  
pp. 16005
Author(s):  
Hansini Mallikarachchi ◽  
Kenichi Soga
Keyword(s):  
Shear Band ◽  
Constitutive Model ◽  
Bifurcation Analysis ◽  
Shear Bands ◽  
Constitutive Relationship ◽  
Excess Pore Pressure ◽  
Biaxial Compression ◽  
Compression Tests ◽  
Equilibrium Equations ◽  
Dense Sand

When saturated granular materials which are dilative in nature are subjected to the undrained deformation, their strength increases due to the generation of negative excess pore pressure. This phenomenon is known as dilative hardening and can be witnessed in saturated dense sand or rocks during very fast loading. However, experimental evidence of undrained biaxial compression tests of dense sand shows a limit to this dilative hardening due to the formation of shear bands. There is no consensus in the literature about the mechanism which triggers these shear bands in the dense dilative sand under isochoric constraint. The possible theoretical reasoning is the local drainage inside the specimen under the globally undrained condition, which is challenging to be monitored experimentally. Hence, both incept of localisation and post-bifurcation of the saturated undrained dense sand demand further numerical investigation. Pathological mesh dependency hinders the ability of the finite element method to represent the localisation without advanced regularisation methods. This paper attempt to provide a macroscopic constitutive behaviour of the undrained deformation of the saturated dense sand in the presence of a locally drained shear band. Discontinuation of dilatant hardening due to partial drainage between the shear band and the adjacent material is integrated into the constitutive model without changing governing equilibrium equations. Initially, a classical bifurcation analysis is conducted to detect the inception and inclination of the shear band based on the underlying drained deformation. Then a post-bifurcation analysis is carried out assuming an embedded drained or partially drained shear band at gauss points which satisfy bifurcation criterion. The smeared shear band approach is utilised to homogenise the constitutive relationship. It is observed that the dilatant hardening in the saturated undrained dense sand is reduced considerably due to the formation of shear bands.

scholarly journals Discrete Element Modeling of Crack Initiation Stress of Marble Based on Griffith’s Strength Theory

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Suifeng Wang ◽  
Fei Tan ◽  
Minglong You ◽  
Yu-Yong Jiao ◽  
Fubin Tu
Keyword(s):  
Crack Initiation ◽  
Particle Flow Code ◽  
Biaxial Compression ◽  
Discrete Element Modeling ◽  
Compression Tests ◽  
Strength Theory ◽  
Evolution Law ◽  
Crack Initiation Stress ◽  
Damage Process ◽  
Initiation Stress

Investigating the crack initiation stress of rocks is vital for understanding the gradual damage process of rocks and the evolution law of internal cracks. In this paper, the particle flow code method is used to conduct biaxial compression tests on a marble model with an elliptical crack under different confining pressures. According to the evolution status of microcracks in the rock during compression, four characteristic stresses are defined to reflect the gradual damage process of the marble. Two different methods are used to obtain crack initiation stress of rocks, and the calculation results are compared with those based on Griffith’s strength theory to verify the accuracy of this theory under compressive stress. Based on the numerical simulation results, the evolution law for the strength parameters of marble with the degree of damage is described. According to the proportional relationship between the peak stress and crack initiation stress, a new method for predicting the initiation stress is proposed, whose effectiveness is verified. Overall, the results of this study can serve as a useful guide for solving the important problems of slab cracking and rockburst encountered in underground space engineering.

scholarly journals Study on Hysteretic Fracture of Naturally Cracked Surrounding Rock

2015 ◽  
Vol 2015 ◽  
pp. 1-11
Author(s):  
Zhibin Zhong ◽  
Ronggui Deng ◽  
Fang Lin ◽  
Ying Zhang ◽  
Lei Lv ◽  
...  
Keyword(s):  
Laboratory Test ◽  
Vertical Displacement ◽  
Fracture Pattern ◽  
Surrounding Rock ◽  
Numerical Results ◽  
Tensile Fracture ◽  
Biaxial Compression ◽  
Compression Tests ◽  
Initial Fracture ◽  
Distribution Of Stress

To determine the hysteretic fracture mechanism of the hard and naturally cracked surrounding rock mass, uniaxial and biaxial compression tests were performed on rhyolite specimens. In the biaxial compression test, displacements and strains around the U-shaped opening were monitored throughout to study the fracture pattern and distribution of stress. To compare with the experimental results, the finite difference codeFLAC3Dwas used to simulate a perfectly intact rock model with the same geometric and mechanical conditions in a continuum model. Stress-strain curves under uniaxial compression and the surrounding rock stresses of numerical results were compared with laboratory test. On one hand, laboratory test and numerical results all showed that tensile fracture regions were found at the crown and floor of the opening while shear regions are found at the sidewall. On the other hand, due to microcracks in the laboratory specimen, the laboratory test showed lower ultimate compressive strength. However, its vertical displacement of initial fracture was larger than those of numerical model which did not consider about the microcracks. They revealed the hysteretic fracture behaviour of underground opening in hard and cracked rock.

scholarly journals Acoustic Emission Characteristics and Failure Mechanism of Fractured Rock under Different Loading Rates

2017 ◽  
Vol 2017 ◽  
pp. 1-13 ◽  
Author(s):  
Yongzheng Zhang ◽  
Gang Wang ◽  
Yujing Jiang ◽  
Shugang Wang ◽  
Honghua Zhao ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Failure Mechanism ◽  
Strain Energy ◽  
Loading Rate ◽  
Fractured Rock ◽  
Acoustic Emissions ◽  
Biaxial Compression ◽  
Particle Model ◽  
Energy Rate ◽  
Loading Rates

To study the loading rate dependence of acoustic emissions and the failure mechanism of fractured rock, biaxial compression tests performed on granite were numerically simulated using the bonded particle model in Particle Flow Code (PFC). Uniaxial tests on a sample containing a single open fracture were simulated under different loading rates ranging from 0.005 to 0.5 m/s. Our results demonstrate the following. (1) The overall trends of stress and strain changes are not affected by the loading rate; the loading rate only affects the strain required to reach each stage. (2) The strain energy rate and acoustic emission (AE) events are affected by the loading rate in fractured rock. With an increase in the loading rate, AE events and the strain energy rate initially increase and then decrease, forming a fluctuating trend. (3) Under an external load, the particles within a specimen are constantly squeezed, rotated, and displaced. This process is accompanied by energy dissipation via the production of internal tensile and shear cracks; their propagation and coalescence result in the formation of a macroscopic rupture zone.

Effects of Rolling Resistance on Shear Behavior and Anisotropy of Granular Matters

2013 ◽  
Vol 631-632 ◽  
pp. 198-204
Author(s):  
Yi Ming Liu ◽  
Hai Jun Mao ◽  
Chun He Yang
Keyword(s):  
Shear Strength ◽  
Discrete Element Method ◽  
Numerical Simulations ◽  
Rolling Resistance ◽  
Discrete Element ◽  
Shear Behavior ◽  
Contact Model ◽  
Biaxial Compression ◽  
Compression Tests ◽  
Dramatic Effect

Standard discrete element method does not take the effect of rolling resistance into account. To overcome this shortcoming, a contact model considering rolling resistance is developed and implemented into PFC2D. Using this contact model, a series of numerical biaxial compression tests are carried out. The results of these numerical simulations show that rolling resistance has remarkable effects on shear strength and shear dilatancy of granular matters, and these trends are agreed with previous studies, which proves that this model works well. Then the effect of rolling resistance on anisotropy of granular matters is studied in this paper. It can be seen that rolling resistance has dramatic effect on the anisotropy of granular matters. The anisotropy of granular matters increases with rolling resistance.

scholarly journals Prediction of Shear Localisation in Granular Materials based on a Critical State Non-coaxial Model

2019 ◽  
Vol 92 ◽  
pp. 16006 ◽  
Author(s):  
Hansini Mallikarachchi ◽  
Kenichi Soga
Keyword(s):  
Granular Materials ◽  
Plane Strain ◽  
Critical State ◽  
Progressive Failure ◽  
Shear Bands ◽  
State Parameter ◽  
Biaxial Compression ◽  
Compression Tests ◽  
Principal Axes ◽  
Shear Localisation

Experimental evidence indicates that the shear localisation acts as a precursor to the failure in biaxial compression tests of granular materials. Once formed they are persistent and lead to progressive failure of most geotechnical structures. It is generally accepted that the primary mode of deformation within these shear bands is simple shear which is accompanied by rotation of principal axes. Hence, the conventional plasticity theories based on the assumption of coaxility is not sufficient to describe the behaviour within those shear bands. This paper highlights the influence of the non-coaxility on the initiation and orientation of shear bands in both drained and undrained sand. The con-coaxial plasticity theory is integrated into a critical state constitutive model enriched with the state parameter concept. The model is capable of taking account of the variation of lode angle under plane strain condition. Numerical plane strain biaxial compression tests are conducted to observe the effect of non-coaxility on shear localisation. Bifurcation criteria based on the acoustic tensor are checked to predict the onset and inclination of the shear band. Predictions from the non-coaxial model are compared with those of coaxial model. The influence of the initial void ratio for the formation of shear bands is explored. Results are compared qualitatively with experimental observations.

scholarly journals THE CIRCUMFERENTIAL MECHANICAL PROPERTIES OF BAMBOO WITH UNIAXIAL AND BIAXIAL COMPRESSION TESTS

BioResources ◽  
2012 ◽  
Vol 7 (4) ◽  
Author(s):  
Zehui Jiang ◽  
Fuming Chen ◽  
Ge Wang ◽  
Xing'e Liu ◽  
Sheldon Q. Shi ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Biaxial Compression ◽  
Compression Tests
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